1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to an active matrix type of liquid crystal display device.
2. Description of the Related Art
An active matrix type of liquid crystal display device is characterized by a structure in which a switching element made of, for example, a thin-film transistor (TFT) is incorporated in each pixel of its liquid crystal display panel.
The active matrix type of liquid crystal display device has, as a chamber for a liquid crystal, a pair of substrates (at least one of which is a so-called transparent substrate having a sufficient optical transmissivity) which are arranged to oppose each other across the liquid crystal, and a pixel group is formed in a direction in which the liquid crystal is spread along the main surface of this substrate. This pixel group includes pixels each of which is provided in a portion surrounded by two adjacent ones of a plurality of scanning signal lines formed over the main surface of one of the pair of substrates which faces the liquid crystal (a liquid crystal layer) and by two adjacent ones of a plurality of video signal lines formed to cross the plurality of scanning signal lines. Each of the pixels is provided with a switching element to be driven by a scanning signal supplied from one of the two adjacent scanning signal lines and a pixel electrode to which a video signal supplied from one of the two adjacent video signal lines via this switching element is to be applied.
In this structure, a signal from a scanning driving circuit is inputted from one end of each of the scanning signal lines, while a signal from a video signal driving circuit is inputted from one end of each of the video signal lines. These driving circuits are mounted on the periphery of one of the substrates (the transparent substrate).
Each of the driving circuits is arranged to receive an input signal from a control circuit or the like which is mounted on, for example, a printed circuit board, but in this case, the transmission of signals to the driving circuits is effected by a flexible wiring board connected between the printed circuit board and one of the substrates of the liquid crystal display panel (for example, the transparent substrate on which the driving circuits are mounted).
The aforementioned flexible wiring board (also called xe2x80x9cthe flexible printed circuit boardxe2x80x9d, or xe2x80x9cFPCxe2x80x9d as its abbreviation) being utilized for the liquid crystal display device is disclosed in e.g. the Japanese Patent Laid-Open Nos. 270814/1995, 123489/1998, 38430/1999, and 52409/1999.
However, in a trend toward an increase in the size of the liquid crystal display device constructed in the above-described manner, it has been pointed out that a defective connection occasionally occurs between the flexible wiring board and one transparent substrate of the liquid crystal display panel.
In the above-described liquid crystal display device, one of the pair of substrates (for example, the transparent substrate) and the flexible wiring board are constructed so that each of interconnecting terminals formed on the substrate and the corresponding one of interconnecting terminals formed on the flexible wiring board are opposed and connected to each other. It has been found out that if the flexible wiring board is thermally expanded, the positions of the interconnecting terminals formed on the flexible wiring board deviate from those of the corresponding interconnecting terminals formed on the transparent substrate.
Measures against this deviation have become indispensable because the deviation becomes larger in proportion to-an increase in the size of the liquid crystal display device (to be exact, the liquid crystal display panel).
It has also been found out that the harmful effect of thermal expansion of the flexible wiring board occurs not only while the flexible wiring board is being connected to one of the transparent substrates of the liquid crystal display panel, but also after the flexible wiring board has been connected.
This is because even after the flexible wiring board has been correctly connected, the connecting portions of the flexible wiring board may peel due to an expansion of the flexible wiring board.
Moreover, in the trend toward an increase in the size of the liquid crystal display device constructed in the above-described manner, it has been pointed out that a waveform distortion easily occurs in a video signal which is transmitted through a video signal line or lines located on one side in the direction of juxtaposition of video signal lines among a plurality of video signal lines juxtaposed over the main surface of the substrate.
In the case of a structure in which signals are supplied from the control circuit to the respective driving circuits via the flexible wiring board, it has been found out that a video signal transmitted to a video signal line which is distant from the control circuit suffers a distortion in its signal waveform during the process of transmission by the influence of another connected driving circuit.
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a liquid crystal display device which is suitable for preventing the defective connection of a flexible wiring board to a transparent substrate of a liquid crystal display panel in spite of an increase in the size of the liquid crystal display panel.
Another object of the present invention is to provide a liquid crystal display device which is suitable for preventing, in spite of an increase in the size of the liquid crystal display panel, the waveform distortion of a signal transmitted to a signal line which is located on one side of the liquid crystal display panel in the direction of juxtaposition of signal lines, among a plurality of signal lines juxtaposed on the main surface of the substrate.
Representative features of the invention disclosed in the present application will be described below in brief.
 less than Means 1 greater than 
A liquid crystal display device comprises:
a liquid crystal display panel having a liquid crystal (a liquid crystal layer), a pair of substrates (at least one of which is a so-called transparent substrate) arranged to oppose each other across the liquid crystal to constitute a chamber for the liquid crystal, and a plurality of pixels arranged along a spreading direction of the liquid crystal;
driving circuits juxtaposed on the liquid crystal display panel (one of the pair of substrates), for supplying video signals or scanning signals to the plurality of pixels; and
a flexible wiring board extended along a direction in which the plurality of driving circuits arc juxtaposed, for supplying signals to input sides of the plurality of driving circuits, respectively, from a control circuit (which is mounted on, for example, a printed circuit board such as a control circuit board),
wherein a structure for relaxing thermal expansion is adopted in a portion of the flexible wiring board on a side thereof connected to the driving circuits with respect to the extension direction of the flexible wiring board. This structure need not necessarily be applied to a portion which is located on the opposite side to the aforesaid portion with respect to the extension direction. One specific example of this structure is that the flexible wiring board is:divided into plurality along the extension direction.
In the liquid crystal display device constructed in this manner, because the length of the flexible wiring board (for example, the overall longitudinal length) is shorter than that in a conventional structure, even if the flexible wiring board is thermally expanded, it is possible to reduce thermal stress which occurs in the connecting portions between the flexible wiring board and the driving circuits.
Accordingly, in spite of an increase in the size of the liquid crystal display panel, it is possible to prevent the defective connection of the flexible wiring board to the transparent substrate of the liquid crystal display panel.
 less than Means 2 greater than 
In the liquid crystal display device of the above-described means 1, the control circuit is characterized by being constructed so that a signal is supplied from the control circuit to each of the flexible wiring boards.
In accordance with the liquid crystal display device constructed in this manner, the distances from the connecting portion of each of the flexible wiring boards to the most distant signal line and to the neighboring signal line or lines arc shorter than those in the conventional structure, whereby it is possible to prevent occurrence of the waveform distortion of signals to be supplied to the signal lines. The capacity of the interconnecting lines of the flexible wiring board arc increased by the driving circuits in which circuits which repeat charging and discharging are incorporated, but such capacity can be decreased to a great extent because the number of the driving circuits 6 can be reduced to half by using the above-described structure.
Accordingly, in spite of an increase in the size of the liquid crystal display panel, it is possible to prevent waveform distortion from occurring in a signal on a signal line which lies on one side of the liquid crystal display panel in the direction of juxtaposition of the signal lines.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.